(Portland, OR)  --  The city of Portland, Oregon says Uber used software to evade 16 government officials trying to regulate the service.  City officials say an investigation found that Uber used a software tool called Greyball that blocked regulators from booking rides.  Uber began using Greyball in December 2014, when it didn't have permits in Portland, and stopped using it when it got city approval in April 2015.  An Uber spokesman said the company is pleased that the investigation is over.  A city official said Portland will make sure that no attempts to evade regulators will be allowed in the future.